In this study we utilize results from Swedish students in PISA 2003 and 2006 to examine what types of task properties predict the demand of reading ability of a task. In particular, readability properties (sentence length, word length, common words, and information density) and task type properties (content, competence, and format) are examined. The results show that it is primarily readability properties of a task that predict the task’s demand of reading ability, in particular word length and to some extent information density (measured through the noun-verb quotient).